Knowledge of proteins is important in drug design, protein engineering, and material science. For example, knowing the precise structure of such complex molecules provides a key to understanding their biological function and can lead to methods of altering or controlling the function in ways that result in new drugs or better drugs.
It is through sophisticated x-ray diffraction analysis of a protein in crystallized form that scientists are able to construct a model of the molecular structure of a protein. Unfortunately, protein crystals grown on earth are often small and flawed. However, it has been shown on previous space shuttle missions that protein crystals grown in low gravity can produce superior crystals for such analysis. In particular, in low gravity environments of the orbiting space shuttle, the effects of sedimentation and convection are nearly eliminated during crystal growth of such proteins.
One article describing a previous low gravity system for growing crystals was carried in the Huntsville Times on Sept. 27, 1987 and entitled "Next Shuttle Flight to Carry Alabama Experiments". This article described a device in which twenty sample chambers were provided. By operation of a crank, plugs for the double barreled syringes in the chambers were simultaneously moved from the double barrel tips while the contents of the syringes were pushed from the tip. A separate reservoir was provided into which water was drawn to concentrate the protein in the droplets formed at the end of the tip. Upon completion of the experiment, the crank was then turned in the opposite direction to simultaneously withdraw the solution back into the syringe and plug the syringe for the flight back to earth.
Another disclosure of a protein crystal growth experiment apparatus is contained in a NASA/Marshall Space Flight Center handout dated January, 1988. This handout discloses the use of a vapor diffusion apparatus tray loaded in a carrier which is then mounted in a refrigerator-incubator module. The vapor diffusion apparatus tray contains twenty experiments with each experiment chamber having a protein solution and a precipitant solution held in two separate barrels of a syringe. The solutions are extruded from the syringe to form a single drop which then hangs suspended over a reservoir of precipitant solution of higher concentration. A ganging mechanism operates the twenty experiments in each tray simultaneously. After a predetermined growth period, the droplets are retracted into the syringe and the syringe can be plugged or left unplugged.